For a so-called split mold in which a tread ring comprises plural sector molds separately formed in the circumferential direction, it is widely known, as conventional technique for venting air in the mold, to provide vent holes in the sector molds themselves.
In this technique, the rubber penetrates into the vent holes to yield whisker-like spews which spoils the appearance of the tire thereby requiring a special processing step for cutting and removing a number of spews. Thus, as shown in FIG. 1 by way of example, it is recently proposed to vent air through minute gaps δ between plural fixed molding pieces 22 which are provided on an inner surface side of each sector mold 21 and are circumferentially aligned with each other. In this case, it is considered to be advantageous to improve the capacity of venting air, that vacuum suction means are connected to the minute gaps for a forced ventilation.
In the conventional technique in which air is vented through between the fixed molding pieces 22, however, the piece gaps δ are set to be a small given value so as to prevent the rubber from flowing out and hence the capacity of venting is lower than that of venting air by means of the vent holes, which tends to cause a drawback in the appearance such as bares. This drawback cannot be thoroughly solved due to the piece gaps being too small even though the forced ventilation is carried out by the vacuum suction means.
Further in this case, since the rubber penetrates into the piece gaps δ and hence the gap δ is plugged in the early stage to lower the capacity of venting air, there is a problem that cleaning the mold at a short cycle is inevitable.
The present invention is aimed to solve the above-mentioned drawback of the conventional technique, and an object thereof is to provide a vulcanizing mold for a tire in which the capacity of venting air through between the molding pieces of the sector mold is significantly enhanced to eliminate a possibility of causing the defective appearance such as bares even though almost all or all of the vent holes is removed.